Manufacture of potassium nitrate



MANUFACTURE OF POTASSIUM NITRATE Filed July 22, 1932 FIQW mm Oxygen l$ylwnii/2: P0- Nifmus ases fassium Crude Salt Amm aniaz v v b v MirmedPOttZS- Circulafing e 27? 6' j Mmher' Lye 31 h Residue g H01 SolutionPeta ss iu m i Nitrate in van mm:

MW. WA/WW Patented Mar. 31, 1936 UNITED STATES 2,035,804 MANUFACTURE OFPOTASSIUM NIT-RATE Karl Haase and Hellmu Hartz, Germany,

t Werth, Bleicherode on assignors, by .mesne assignments, to the firm:Preu ssische Bergwerksund Hiitten Aktiengesellschaft, Berlin, GermanyApplication July 22, 1932, Serial No. 624,140 In Germany June 15, 1932 jClaims.

This invention has reference to the manufacture of potassium nitratefrom crude potassium salts, such as for instance from the so-calledsylvinite or from suitable artificial or otherwise obtained saltmixtures by the nitration thereof and by conversion inaqueous solution.In an exemplification of the principles of the invention we may forinstance preferably proceed by carrying out the nitration of the crudepotassium salts, such as sylvinite and similar salt mixtures, to thedesired degree by means of nitrous gases obtained in the combustion ofammoniaflthis nitrating process being for instance performed with thedry salt, whereupon the nitrated salt in the second stage of the newprocess is treated with such salt solutions as will allow of convertingpractically all of the nitrates obtained into potassium nitrate. Afterthe separation of the solid potassium nitrate the salt liquor may beused over again in the same cycle of operations for theconversion of newquantities of nitrated crude salts. By means of this method of procedureit becomes possible to manufacture potassium nitrate directly from twocomparatively cheap raw products, that is to say from crude potassiumsalts and from the gases of combustion of the oxidation of ammonia; in ashort time and in a continuous highly economical and mechanically simplemanner.

In accordance with the previous stateof the art, finished'manufacturingproducts have been employed as the starting material exclusively orin'part, and this was the main cause for the high costs and thedifi'iculties of manufacture of this valuable fertilizing substancewhich has to be produced by 'mass-manufacturing means. This drawback isshared by all methods which make use of nitric acid or of nitratesobtained from nitric acid as the origin of nitrogen, such as forinstance nitrate of sodium, nitrate of magnesium, aluminium nitrate andthe like, while the potassium basis is obtained from chloride or sulfateof potassium.

With the employment of liquid nitric acid these methods present theadditional difliculty of necessitating a number of pieces of apparatus,the costs and operation of which are highly expensive and out of allproportion'with the general price of commodities; besides, such kinds ofapparatus, in spite of their being protected by acidproof material, aresubject to a very substantial heavy wear. For the purpose of cheapeningand simplifying the manufacture of potassium nitrate it has already beensuggested to employ at least one of the components from which potassiumnitrate is obtained on a large scale in the form of incomplete or rawmanufacturing products. Thus, it has already been attempted for instanceto utilize the mutual reaction of 5 potassium crude salts with sodiumnitrate in aqueous solution; but, even with this suggestion there is thedrawback that a finished manufacturing product is necessitated whichmust either be bought abroad or must be manufacl0 tured synthetically bymeans of nitric acid. It has'also been suggested heretofore to replacethe nitric acid by the intermediate product of the manufacture of nitricacid, that is to say,

to utilizethe nitrous gases for this purpose and 15 the crude potassiumsalts directly owing to the want of suitable direct processes ofextraction and conversion, so that in this case also a finishedmanufacturing product had to be used as the potassium base. With thismethod there was the additional inconvenience that, with the 25 use ofpotassium chloride the reaction with oxides of nitrogen proceeded veryslowly so that the conversion into potassium nitrate was finished onlyafter several days treatment, so

that this mode of manufacture was highly 3o unec'onomical andunsatisfactory.

In orderto make our invention more clear, we refer to the accompanyingdrawing on which a flow-table is shown which will be dealt with indetail hereinafter. Prior, thereto, however, certain statements andexplanations are necessary, as'follows:

Now the process of this invention is distinguished from this state ofthe art by the fact that it"utilizes exclusively such kinds of 40starting -material which constitute cheap raw products and theconversion thereof into potassium nitrate makes it possible to dispensewith the necessity of employing the finished preliminary manufacturingproducts referred to;

and there is the additional advantage that it makes use of an operatingmethod which allows of the manufacture of potassium nitrate in simple,inexpensive pieces of apparatus which are subject to a very low degreeof Wear only.

In practising this method of manufacture it has been ascertained that bythe employment of raw potassium salts in the place of potassium chlorideand by the subdivision of the process of. production into two stages, ofwhich one is period of time than it has been possible with the processesheretofore in use.

Thus, it has been ascertained that, while the manufacture of potassiumnitrate according to the well-known processes using potassium chlorideeven with the use of nitrous gases took five to six days as a result ofthe retardation of the reaction, particularly towards the end of thereaction procedure, the manufacture of this valuable fertilizer inaccordance with the process of this invention is reduced'to buta'fraction of the period otherwise required. In accordance with thisinvention the favorable results and the reduction of the working periodare moreover assisted by the only partial nitration of the chloridecompounds of the crude potassium salt parts by weight of crude saltcontain, for instance, 25 parts by weight of KCl, 20 to 25 parts byweight of CaSO4, 50 to 55 parts by weight of NaCl) with the aid of theutilization of the higher conversion speed at the commencement of everyreaction in the first section of the process (nitration) and by furthertreat ment of the thus prepared product on an aqueous way with a certaindefinite'assistance of the reaction by a supply of heat in the secondsection of the process (conversion).

The entire process of nitration of the crude potassium salt according tothis invention, using for instance a salt with a content of 22 to 23percent of potassium chloride, is ordinarily terminated after about 10hours and may even be reduced to 6 hours, if required, by the use ofpure dioxide of nitrogen, while the succeeding, continuously operateddissolving or conversion stage may also be carried out in a few hours.

In the first stage of the process ground crude potassium salt, as forinstance ground sylvinite, which may even contain small amounts ofcarnallite is treated in this state or in the agglomerated conditionwith nitrous gases, such as are formed by the combustion of ammonia, attemperatures above 100 C. This treatment may for instance be effected ina furnace provided with indirectly heatable false bottoms of the type ofthe so-called I-Ierreshoif-furnaces, as for'instance in a scooping drieror steam-plate drier used in plants for the preparation of combustiblecoal or the like. In such a kind of furnace the nitration may beeifected in a continuous process, the crude salt and the oxidesof'nitrogen being preferably caused to move in the counter-currentdirection. The chlorides contained in the crude salt are therebyconverted into nitrates, liberating chlorine which latter combines withthe excess of oxides of nitrogen to form nitrosyl-chloride. It isimmaterial for the success of the process of this invention which of theexisting chlorides of the salt are converted into nitrates, and it ismoreover of no importance which of the existing chlorides is to beconverted into nitrate audit is likewise of no importance whether theone. or the other is more or less nitrated, provided that the entireabsorption of nitrogen in the form of N03 is at least equivalent to theamount of potassium chloride originally present. Preferably, theoperation is carried out in such a manner that the v ,Ki': NO3=1: 1required for the subsequent conversion may be obtained. Thenitrosyl-chloride obtained may be treated by well-known methods for therecovery of the oxide of nitrogen.

In the second stage of the process according to this invention thenitrated crude salt is treated with a suitable preheated salt solutionin any suitable dissolving apparatus, using for instance those kinds ofdissolving apparatus Which are used in the potassium-industry. Thenitrates formed in the nitrating stage are thereby dissolved andconverted into KNOB. In the practice of this invention the compositionand the quantity of the salt solution are so adjusted that a solution isobtained which is saturated as regards KNOz, KCl and NaCl and which maybe easily separated from the'undissolved admixtures. Counter to theusual expectations it has been ascertained in this connection thatheating of the solution above certain temperatures for the purpose ofconversion and for obtaining a potassium-nitrate of about 96% is notnecessary, inasmuch as even with temperatures of 50 to 70 C. forinstance and in special, particularly investigated cases at 60 C., thereaction is going on with sufficient rapidity and the conditions areparticularly favorable for the separation of the solid admixtures. Theprocess according to this invention presents therefore the additionaladvantage of a very considerable economy of heat, as compared with knownmethods in which the conversion of crude salt and the like is carriedout at an increased temperature.

The further procedure of the second stage of the process is simple.After the separation of the residue which contains mostly NaCl and CaSOrthe hot solution which contains the entire amount of the potassium,introduced with the. crude salt and the entire amount of the nitrogen ofthe nitrate in the form of KNOs is mixed with a quantity of watercorresponding to that amount which is lost in the residue by adheringliquid and by evaporation and is cooled. This results in theprecipitation of a high-grade kind of potassium-nitrate, and amother-liquor is obtained, the composition and quantity of whichcorresponds to the original salt solution and which may be used again asa solvent liquid, so as to constitute a cycle of the utilization of themother-liquor. Preferably, the operation is carried out incounter-current direction. Whenever required, this potassium nitrateobtained according to this invention may be treated in the well-knownmanner by lixiviation with some water so as to obtain absolutely pureKNO3.

In the following we describe the above-mentioned flow-sheet, on whichthe substances playing parts in the entire process are arranged, andfollow one another, like a cycle, indicated in this case by quadranglesrepresenting said-substances and by connecting lines indicating theirflow. The details are as follows: Oxygen (quadrangle a) and ammonia(quadrangle b) are burned together in any of the known apparatus usuallyemployed for this purpose' There arise V to act upon sylvinite potassiumx-cru-de asalt (quadrangle d) in any of the furnaces mentionedin theprecedingpart of thisspecification. The product of this phase of theprocess isnitrated potassium crude salt (quadrangle e) which, afterhaving been: removed from the reaction apparatus employed for carryingout this phase, is continually conducted into the-dissolving apparatuslikewise mentioned by way of example in the preceding part of' 'thisspecification, in which apparatus saidnitrated-potassium crude salt istreated in counter-current=with:preheated mother-lye (quadrangle f),themixture being stirred during this treatment. There is obtained a hotsolution (quadrangle'g) which has taken up the nitrated portionsiof saidcrude salt, or has converted it into KNOaand besides this compound isobtained a residue formed by unchanged, insoluble crude salt(quadrangleh). This residue is separated from saidhot solution bysuitable means whereafter the solution is cooled, in consequence whereofpotassium nitrate precipitates. This is thefin'al product, the substanceintended, that is to beturned into account. The remaining liquidconstitutes the mother-lye that then is-heated in a suitable apparatusand is conducted to the already mentioned mother-lye (quadrangle f),the-lye mixture being then again used in connection with the nitratedpotassium crude saltso as todeliver again a hot solution and a residue,as described. The aqueous salt solution circulates; therefore,continuously through the phases 1 and g; constituting circulating motherlye -in the phase 1 and an aqueous hot salt solution in the phase 9.

It should be pointed out that it could-not-be expected that by the useof crude salt of potassium and the like as a starting material, thoughit contains foreign substances, the nitration could be carried out onthe dry-way and ina highly satisfactory manner, and that an availableproduct for the manufactureof potassiumnitrate could be obtained by anaqueous liquid inasmuch as it was the general'opinion thatyfor thepurpose of accomplishing this result, it was necessary to employexclusively a sufliciently pure starting material, such as manufacturedby the potassium industry in the form of potassiumchloride and potassiumsulfate. -'-Nor was it to be anticipated that the nitrated crudesalt-would yield potassium nitrate of sufiicient purity by the solutionand conversion of the nitrates obtained in the nitrating stage and at adissolving temperature of for' instance 60 0., nor that the convertingor finishing solution could be used in a cycle of operations forthe'manufacture' of new quantities of nitrate without any reduction ofvolume by evaporation and without the elimination of constituent partsof the motherliquor. It is, moreover, an unexpected result that thetime-consuming complete nitration'of chloride of potassium could-bereplaced by a dry and merely partial nitration of the chlorides of thecrude salt with the subsequent treatment by an aqueous solution at agreat economy of costs and operating time.

Experimental Example 1.-68 grams of most finely ground sylvinite with22% of potassium chloride are treated for 10 hours at 150 C. with acurrent of nitrous gases, such as are obtained in the combustion ofammonia. The yield was 73 grams of a neutral dry salt mixture containing10.83% of potassium and 3.968% of nitrogen in the form of differentnitrates. The product which contains potassium and'nitrogen inthemolecular proportion of 1:1.02 was mixed with non-nitrated-sylvinite orwith potassium-chlorideso' as to present equimolecular quantities and:was then treated in accordance with EX- ample 3 described hereinafter,and worked into potassium-nitrate. The nitrosyl-chloride evolved upon"the nitration of the crude salt can be recovered and worked into oxidesof nitrogen in thewell-known manner.

"Example:'2.--68 grams of most finely ground sylvinite with 22.8% ofpotassium chloride were treated :for 6 hours at 150 C., and inaccordance with the Example 1 with a current of pure concentrateddioxide of nitrogen. A yield of '73 gramsofa .salt mixture with 11.09%of potassium and 3.973% of nitrogen as nitrate was obtained. The productwhich contains potassium and the nitrogen of the nitrate in themolecular proportion 1:1 may be worked into potassium nitrate inaccordance with Example 3 now being described.

Example 32-1362 grams of sylvinite that has been nitrated in accordancewith Example 1 or Example 2 and containing molecularly equal quantitiesof potassium and of nitrogen with 12.03% 'of potassium and 4.309% ofnitratenitrogen are stirred a short time into one liter of asaltsolution of the specific gravity 1.33 which contains in one literapproximately: 188 grams of 'KNOs, 81' grams of NaNOs, 148 grams ofNaCI, 111 grams of MgClz, and 10 grams of CaSO4, at about 60 C. The hotsolution obtained was separated from the residue and cooled to 20 C.,with the addition of about 99 cc. of water. The precipitatedpotassium-nitrate was filtered oif and dried. The yield amounted to 428grams of potassium nitrate of 96% and one liter of a salt solution ofthe composition above stated which could beused over again for thepurpose of conversion.

It should be noted that our invention is not to be restricted to certaindetails of treatment and tea certain nature and proportions of materialsheretofore referred to merely by way of exemplification and illustrationof the principles of'the invention, this latter being susceptible ofmodifications and variations both in the nature and in the proportionsof material employed and in the mode of treatment, no other limitationsbeing warranted and intended, except those which appear from the claimshereunto appended.

We claim:

1. The process of manufacturing potassium nitrate, comprising subjectingsalt in a dry way and at a temperature of more than 100 C; to a partialnitration with nitrous gases: obtained in known manner; interrupting thenitration of said salt at a point of time at which the entire absorptionof nitrogen in the form of N03 is at least equivalent to the amount ofpotassium chloride originally present; treating. the reaction productwith an aqueous salt solution containing nitrate ions; and separatingthe potassium nitrate thereby formed by crystallization, substantiallyas set forth.

2; The process of manufacturing potassium nitrate, comprising subjectingcrude potassium salt in a dry Way and at a temperature of more than 100C. to a partial nitration with nitrous gases obtained in known manner;interrupting the nitration of said salt at a point of time at which theentire absorption of nitrogen in the form of N05 is at least equivalentto the amount of potassium chloride originally present; treating thereaction productin known manner with mother liquor obtained fromapreceding' cycle of similar phases of operation, and separating thepotassium nitrate thereby iormed by crys-. tallization.

3. The process of manufacturing potassium nitrate, comprising subjectingcrude potassium salt in a dry way and at a temperature of more than 100C. to a partial nitration with nitrous gases obtained in known manner;interrupting the nitration of said salt at a point of time at which theentire absorption of nitrogen in. the form of N03 is at least equivalentto the amount of potassium chloride originally present; treating thereaction product in known manner with mother liquor obtained from apreceding, cycle of similar phases of operation; separating from thesolution in known manner the undissolved residual substances, andcooling the remaining solution so as to obtain the potassium nitrate incrystalline form.

4. The process of manufacturing potassium nitrate, which comprisessubmitting crude salt minerals containing potassium salts to a partialnitration so as to cause the conversion of the K01 to KNO3 withoutmaterial conversion of the other chloride in the salt and subsequentlytreating the reaction product with an aqueous mixture containingwater-soluble alkali salts of sufficient concentration; separating andcooling the solution of the potassium nitrate, and cans-- ing the saidnitrate to become separated and crystallized therefrom, and finallytreating new quantities of nitrated salt minerals with the mother-liquorobtained.

5. The process of manufacturing potassium nitrate with the aid of amother lye obtained from a preceding cycle of phases of operationsimilar to those hereinafter stated, said method comprising submitting asolid crude salt mineral containing potassium salts to a'partialsubstantially dry nitration to such an extent as to cause the resultingnitration product to contain potassium and the nitrate radical (N03) inequimolecular quantities, and then treating said product with an aqueoussalt solution identical with said mother liquor, thereby causing thebase of other existing nitrates to become exchanged against thepotassium base, and sepa-' rating the potassium nitrate formed.

6. The process of manufacturing potassium nitrate, which comprisessubmitting crude salt minerals containing potassium salts to a partialnitration, interrupting the nitration of said salt at a point of time atwhich the entire absorption of nitrogen in the form of N03 is at leastequivalent to the amount of potassium chloride originally present;treating the reaction product at an elevated temperature with an aqueoussalt mixture containing nitrates of alkali and other water-solublealkali salts; separating the solution from the residue, cooling thesolution obtained, causing the potassium nitrate to precipitate, andtreating new quantities of nitrated mineral salts with the motherliquor.

'7. A process as specified in claim 1, comprising, in combination withthe phases stated in claim 1, effecting the conversion at a temperaturelying between 50 and C. so as to obtain a solution saturated withpotassium nitrate, potassium chloride, and sodium chloride; separatingthe residual substances from said solution, adding as much water as hasbeen lost by exhalation and as adhering solution in the residualsubstances, and cooling the obtained so-* lution.

8. A process as specified in claim 1, characterized by the feature thatthe nitration of the starting materials is carried out only so far thatthe product to be nitrated contains equivalent amounts ofv potassium andnitrate which substances are then converted into potassium nitrate.

9. The method of producing potassium nitrate, comprising causing nitrousgases to act upon sylvinite potassium crude salt so as to obtainnitrated potassium crude salt; treating thissalt with heated mother-lyeandstirring at the same time this mixture so as to obtain a hot solutionthat has taken up the portion of nitrate contained in said. nitratedpotassium crude salt, unchanged insoluble salt remaining as residue;separating said hot solution and said unchanged insoluble salt from oneanother, cooling the said hot solution so as to cause precipitation ofthe potassium nitrate and to obtain at the same time mother-lye; heatingthis lye and conducting it back to said nitrated potassium crude salt soas to produce again a hot solution of the kind stated.

10. The method of producing potassium nitrate, comprising burningammonia with oxygen so as to obtain nitrous gases; letting these gasesact upon sylvinite potassium crude salt 50 as to obtain nitratedpotassium crude salt; treating this salt with heated mother-lye andstirring at the same time this mixture so as to obtain a hot solutionthat has taken up the portion of nitrate contained in said nitratedpotassium crude salt; unchanged insoluble salt remaining as residue;separating said hot solution and said unchanged insoluble salt from oneanother, cooling the said hot solution soas to cause precipitation ofthe potassium nitraterand to obtain at the same time mother-lye; heatingthis lye and conducting it back to said nitrated potassium crude salt soas to produce again a hot.

solution of the kind stated.

11. The method of producing potassium nitrate, comprising causingnitrous gases to act upon sylvinite potassium crude salt so as to obtainnitrated potassium crude salt; treating this salt in counter-currentwith heated motherlye and stirring at the same time this mixture so asto obtain a hot solution that has taken up the portion of nitratecontained in said hitrated potassium crude salt; unchanged insolublesalt remaining as residue; separating said hot solution and saidunchanged insoluble salt from one another, cooling the said hot solutionso as to cause precipitation of the potassium nitrate and to obtain atthe same time mother-lye; heating this lye and conducting it back tosaid nitrated potassium crude salt so as to produce again a hot solutionof the kind stated.

12. The method of producing potassium nitrate, comprising causingnitrous gases to act upon sylvinite potassium crude salt so as to obtainnitrated potassium crude salt, said gases and said salt being used insuch proportions relatively to one another that the entire absorption ofnitrogen in the form of N03 is at least equivalent to the amount ofpotassium chloride originally present; treating the nitrated potassiumcrude salt with a heated aqueous salt solution and stirring at the sametime this mixture so as to obtain a hot solution that has taken up theportion of nitrate contained in said nitrated potassium crude salt,unchanged insoluble salt remaining as residue; separating said hotsolution and said unchanged insoluble salt from one another, and coolingthe said hot solution so as to cause precipitation of the potassiumnitrate and to obtain at the same time aqueous salt solution.

13.'I'he method of producing potassium nitrate, comprising causingnitrous gases to act upon sylvinite potassium crude salt, said gases andsaid salt being used in such proportions relatively to one another thatat the termination of said action the crude salt contains a somewhatlarger amount of nitrate than would correspond to the original contentsof KCl; treating the nitrated potassium crude salt with a heated aqueoussalt solution and stirring at the same time this mixture so as to obtaina hot solution that has taken up the portion of nitrate contained insaid nitrated potassium crude salt, unchanged insoluble salt remainingas residue; separating said hot solution and said unchanged insolublesalt from one another, and cooling the said hot solution so as to causeprecipitation of the potassium nitrate and to obtain at the same timeaqueous salt solution.

14. The method of producing potassium nitrate, comprising causingnitrous gases to act upon sylvinite potassium crude salt, said gases andsaid salt being used in such proportions relatively to one another thatat the termination of said action the crude salt contains a somewhatlarger amount of nitrate than would correspond to the original contentsof KCl; admixing at'the end of the nitrating phase nonnitrated crudesalt so as to eliminate the small excess of nitrate, the amounts beingso chosen that the equimolecular proportion K:NO3=1:1

is obtained; treating the nitrated potassium crude salt with a heatedaqueous salt solution and stirring at the same time this mixture so asto obtain a hot solution that has taken up the portion of nitratecontained in said nitrated potassium crude salt, unchanged insolublesalt remaining as residue; separating said hot solution and saidunchanged insoluble salt from one another and cooling the said hotsolution so as to cause precipitation of the potassium nitrate and toobtain at the same time aqueous salt solution.

15. The method of producing potassium nitrate, comprising, causingnitrous gases to act upon sylvinite potassium crude salt so as to obtainnitrated potassium crude salt; treating this salt with heated mother-lyeand stirring at the same time this mixture so as to obtain an aqueoushot salt solution that has taken up the portion of nitrate contained insaid nitrated potassium crude salt, the amounts of the substancesconcerned being so chosen that said solution is saturated as regardsKNOs, KCl and NaCl; separating nitrated potassium crude salt with aheated aqueous salt solution and stirring at the same time this mixtureso as to obtain a hot solution that has taken up the portion of nitratecontained in said nitrated potassium crude salt, unchanged insolublesalt remaining as residue; separating said hot solution and saidunchanged insoluble salt from one another, and cooling the said hotsolution so as to cause precipitation of the potassium nitrate and toobtain at the same time aqueous salt solution.

KARL HAASE. HELLMUT WERTH.

